Dual Function Fuel Atomizing and Ignition Additives

ABSTRACT

The present disclosure relates to methods and compositions for improving fuel atomization and combustion efficiency comprising fuel additives for use in combustion systems where fuel is injected into the combustion zone under very high pressure

FIELD

The present invention relates to fuel additives for use in combustion systems where fuel is injected into the combustion zone under very high pressure.

BACKGROUND

The stripping of electrons from molecules by physical shear force is a well known phenomenon. In a fuel, additives having electron-releasing substituents on an aromatic ring can be tailored to decrease or increase the ability of that ring to lose electrons due to chemical or physical perturbations. When the substituent's electron pressure on the ring increases to a certain level, the ring loses electrons easily in chemical reactions and becomes oxidized to a radical or a positively charged radical, or a positively charged cation. This charging of the additive molecule can also be achieved when the additive is part of a fuel jet exiting an injector nozzle at extremely high pressures. Therefore a fuel containing such an additive atomizes much better due to high shear forces on the injected jet, and additionally the vaporizing droplets will give a radically charged vapor with enhanced ignition properties.

The present application discloses the development of dual-function atomization and ignition fuel additives for use in combustion systems where fuel is injected into the combustion zone under very high pressure (above 1,000 Bar, or 14,504 psi). The shear forces on the injected fuel composition containing the additive would strip electrons from the additive molecules which would in turn impart a destabilizing charge to the surface of the atomizing fuel to increase the rate of atomization. The resulting fuel vapor from this atomization and vaporization of the fuel jet would be charged, a state which is known to promote ignition. Enhanced atomization and ignition would improve the efficiency of the combustion system, and lower exhaust pollutant levels.

SUMMARY OF THE EMBODIMENTS

An embodiment presented herein provides a fuel composition comprising (a) a major amount of a fuel and (b) a minor amount of an additive composition. The additive composition may comprise at least one fuel additive comprising an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein X— comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring, wherein the at least one second substituent comprises at least one of an alkyl group, an alkoxy group, and an amino group. The at least one fuel additive is present in an amount from about 500 ppm or greater in the fuel composition.

In some embodiments, the at least one second substituent may be attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent.

In some embodiments, the fuel composition may further comprise at least one second fuel additive comprising an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein —X comprises a heteroatom and wherein R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent, wherein the at least one second substituent comprises the structure —X—R, wherein —X— comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group. In some embodiments, the fuel composition provides both enhanced fuel atomization and enhanced fuel ignition.

In some embodiments, the heteroatom may comprise at least one member selected from the group consisting of the group 14 elements, the group 15 elements, and the group 16 elements. In some embodiments, the heteroatom may comprise at least one of nitrogen and oxygen.

In some embodiments, R may comprise at least one of methyl, ethyl, propyl, and isopropyl.

In some embodiments, the at least one second substituent may comprise an alkyl group having up to about 32 carbon atoms, wherein the alkyl group comprises a straight or branched chain, and is saturated or unsaturated. In some embodiments, the at least one second substituent may comprise at least one of methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, and pentyl.

In some embodiments, the aromatic ring may comprise at least one of a monocyclic ring, a polycyclic ring, and a heterocyclic ring. In some embodiments, the aromatic ring may comprise at least one of benzene, naphthalene, and anthracene.

In some embodiments, the additive compound may comprises at least one of a member selected from the group consisting of 2,4,6-trimethyl-N-methylaniline; polymerized 1,2-dihydro-2,2,4-trimethylquinoline; 2-methyl indoline; N,N′-di-sec-butyl-p-phenylenediamine; methyl substituted benzenes; ethyl substituted benzenes; propyl substituted benzenes; isopropyl substituted benzenes; butyl substituted benzenes; and isobutyl substituted benzenes.

In some embodiments, the at least one fuel additive is present in an amount from about 4000 ppm or greater in the fuel composition. In still further embodiments, the at least one fuel additive is present in an amount from about 5000 ppm to about 10,000 ppm in the fuel composition.

In another embodiment, a method for improving fuel ignition, may comprise providing a fuel composition to a combustion system, wherein the fuel composition comprises a fuel and at least one fuel additive, wherein the at least one fuel additive comprises an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure X—R, wherein X comprises a heteroatom and wherein R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent, wherein the at least one second substituent comprises the structure —X—R, wherein —X— comprises a —CH₂— or a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group. The fuel ignition of the fuel composition may be enhanced relative to a fuel free of the at least one fuel additive.

In another embodiment, a method of enhancing fuel atomization, may comprise: (a) providing a fuel composition, wherein the fuel composition comprises a fuel and at least one fuel additive, wherein the at least one fuel additive comprises an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein —X comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring, wherein the at least one second substituent comprises at least one of an alkyl group, an alkoxy group, and an amino group; and (b) delivering the fuel composition to a combustion area of a combustion system, wherein the delivery of the fuel composition to the combustion area causes the fuel composition to experience a shear force sufficient to remove at least one electron from the fuel additive to provide a resulting fuel additive. The fuel atomization of the fuel composition may be enhanced relative to a fuel free of the at least one fuel additive.

In some embodiments, the delivery of the fuel composition to the combustion area is at a pressure greater than about 1000 bar. In some embodiments, the delivery of the fuel composition to the combustion area is at a pressure greater than about 1500 bar. In other embodiments, the delivery of the fuel composition to the combustion area is at a pressure greater than about 2000 bar. In still further embodiments, the pressure is in the range of from about 1000 to about 2500 Bar.

In some embodiments, the resulting fuel additive has been oxidized. In some embodiments, the resulting fuel additive has been oxidized to a radical. In other embodiments, the resulting fuel additive has been oxidized to a positively charged radical. In still further embodiments, the resulting fuel additive has been oxidized to a positively charged cation.

In some embodiments, the combustion area of the combustion system is selected from the group consisting of internal combustion engines, boilers, furnaces, incinerators, jet engines, and rocket engines.

In another embodiment, a method for enhancing fuel ignition may comprise providing to the combustion area of a combustion system a fuel composition comprising a fuel additive, wherein the fuel additive decreases the fuel MON and/or RON.

As used herein, the term “octane number” refers to the percentage, by volume, of iso-octane in a mixture of iso-octane (2,2,4-trimethylpentane, an isomer of octane) and normal heptane that would have the same anti-knocking (i.e., autoignition resistance or anti-detonation) capacity as the fuel in question.

As used herein, the term Research Octane Number (RON) refers to simulated fuel performance under low severity engine operation. As used herein, the term Motor Octane Number (MON) refers to simulated fuel performance under more severe (than RON) engine operation that might be incurred at high speed or high load.

Both numbers are measured with a standardized single cylinder, variable compression ratio engine. For both RON and MON, the engine is operated at a constant speed (RPM's) and the compression ratio is increased until the onset of knocking. For RON engine speed is set at 600 rpm, and for MON engine speed is set at 900 rpm. Also, for MON, the fuel is preheated and variable ignition timing is used to further stress the fuel's knock resistance.

As used herein, the phrase “aromatic ring” is intended to encompass a conjugated planar ring system with delocalized electrons. “Aromatic ring,” as used herein, may describe a monocyclic ring, a polycyclic ring, or a heterocyclic ring. Further “aromatic ring” may be described as joined but not fused aromatic rings. Monocyclic rings may also be described as arenes or aromatic hydrocarbons. Examples of a monocyclic ring include, but are not limited to, benzene, cyclopentene, and cyclopentadiene. Polycyclic rings may also be described as polyaromatic hydrocarbons, polycyclic aromatic hydrocarbons, or polynuclear aromatic hydrocarbons. Polycyclic rings comprise fused aromatic rings where monocyclic rings share connecting bonds. Examples of polycyclic rings include, but not limited to, naphthalene, anthracene, tetracene, or pentacene. Heterocyclic rings may also be described as heteroarenes. Heterocyclic rings contain non-carbon ring atoms, wherein at least one carbon atom of the aromatic ring is replaced by a heteroatom, such as, but not limited to, oxygen, nitrogen, or sulphur. Examples of heterocyclic rings include, but are not limited to, furan, pyridine, benzofuran, isobenzofuran, pyrrole, indole, isoindole, thiophene, benzothiophene, benzo[c]thiophene, imidazole, benzimidazole, purine, pyrazole, indazole, oxazole, benzoxozole, isoxazole, benzisoxazole, thiazole, benzothiazole, quinoline, isoquinoline, pyrazine, quinoxaline, acridine, pyrimidine, quinazoline, pyridazine, or cinnoline.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the present invention, as claimed.

DETAILED DESCRIPTION OF EMBODIMENTS

Fuel injection pressures are constantly on the rise, particularly in diesel engines. This is necessary to improve atomization and mixing with the air charge. An increase in injection pressure involves modifications to the fuel delivery systems in terms of material durability and fuel handling energy management. Higher injection pressures result in better engine efficiency and lower emissions, especially particulate matter.

According to the present disclosure, the ability to engineer fuel additives by modulating the two parameters of electron pressure into an aromatic ring, and disruption of ideal geometries for charge delocalization in an additive molecule, gives a good range of operation to cover different combustion systems.

The present application discloses fuel additive components that provide both the individual functions and the dual-functions of enhanced fuel atomization and enhanced fuel ignition. Further, the fuel additives described herein are suitable for use in compression ignition combustion systems where fuel is injected into the combustion zone under very high pressure (above about 1,000 Bar, or about 14,504 psi). The shear forces on the jet of fuel composition strip electrons from additive molecules in the fuel, which in turn impart a destabilizing charge to the surface of the droplets of atomizing fuel to increase the rate of atomization. The resulting fuel vapor from this atomization is charged, a state which is known to promote ignition. Enhanced atomization and ignition as provided herein improve the efficiency of the combustion system, and lower exhaust pollutant levels.

Thus, embodiments described herein may find application, for example, in compression ignition combustion systems with fuel injection pressures above 1000 Bar and/or atmospheric stationary burner systems for industrial and utility furnaces equipped with high pressure fuel injection systems. Embodiments described herein may also find application in compression ignition combustion systems with fuel injection pressures above about 1500 Bar (or about 22,000 psi), or as another example, above about 2000 Bar (or about 29,000 psi). As a further example, the fuel injection pressures may be from about 1000 Bar to about 2500 Bar.

Fuel atomization may be enhanced by including in a fuel composition, additives comprising an aromatic ring that contains electron releasing substituents on the aromatic ring. The substituents may have the basic structure “—X—R” and may append onto the aromatic ring through either a carbon atom or a heteroatom. X may comprise either a carbon atom or elements of group 14 (e.g., X=carbon, silicon, and the like), group 15 (e.g., X=nitrogen, phosphorus, arsenic, and the like), and group 16 (e.g., X=oxygen, sulfur, selenium, and the like) of the Periodic Table. When X is a heteroatom, R may be an alkyl group such as methyl, ethyl, propyl, isopropyl, and the like. Further R may comprise an alkoxy group such as methoxy or an amino group. When X is a carbon atom, R may be an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, pentyl, and the like. Further, R may have up to about 32 carbon atoms. R may be a straight or branched chain and may be saturated or unsaturated. The core aromatic ring may be a monocyclic ring such as benzene, polycyclic, fused rings such as naphthalene and anthracene, or multiple aromatic rings that are joined but not fused together.

In addition to the aromatic ring compounds disclosed above, other suitable substituents which may be attached to a carbon atom of the aromatic ring may include —NR, —OR (e.g., phenols), —SR, —PR, —AsR, —SeR, —TeR, and —SbR, where R may be hydrogen, an alkyl group, an aryl group, a substituted aryl group, an alkoxy group, or an amino group. R may also cyclize back to the aromatic ring and may be attached to it in, for example, the ortho-position of the ring relative to a first substituent.

Substituents releasing electrons into the aromatic ring cause the ring orbitals to expand and become more diffuse. The ring electrons may orbit much further away from the ring carbon nuclei; and, therefore, are less attracted to the positive charge of the carbon nuclei. Aromatic ring electrons orbiting under these circumstances may be expected to strip away easier, either through chemical oxidation or through physical shear forces such as those exerted on a fuel jet exiting an injector nozzle under high pressure, into an air charge. For fuel atomization, the substituents may be located anywhere on the aromatic ring.

For fuel ignition enhancement, the “—X” of at least one of the “—X—R” substituents, attached to a carbon atom of the aromatic ring, may be a heteroatom such as N, O, and the like. The remaining “—X—R” substituents may be in either the ortho or para position relative to the heteroatom substituent (see Table 1). The ignition enhancing property can be realized by testing the additive in a knock engine. When the change in octane due to the additive is negative, then the additive is an ignition enhancer. Examples of this testing are illustrated in the Table 1. Additive compounds that result in the largest negative change in MON and in (RON+MON)/2 provide enhanced fuel ignition.

In some embodiments, a fuel additive as described herein may comprise an aromatic ring having electron-releasing substituents as described above with the duel function of atomization through electron stripping and ignition enhancement through a large negative octane change. This may also be achieved with a mixture of fuel additives, wherein a first additive is optimized for fuel atomization through electron stripping, and a second additive is optimized for fuel ignition. An example would be an additive mixture of tetraisobutyl benzene and 2-methylindolene, with the former optimized for atomization enhancement and the latter (compound 7 in Table 1) for ignition enhancement.

Examples of suitable additive compounds as described herein may comprise, but are not limited to, an arylamine; a 2,4,6-trimethyl-N-methylaniline; a polymerized 1,2-dihydro-2,2,4-trimethylquinoline; a 2-methyl indoline; an N,N′-di-sec-butyl-p-phenylenediamine; methyl substituted benzenes, ethyl substituted benzenes, propyl substituted benzenes, isopropyl substituted benzenes, butyl substituted benzenes, and isobutyl substituted benzenes.

The fuel additive may be present in an amount from about 500 ppm or greater in a fuel composition. As another example, the fuel additive may be present in an amount from about 4000 ppm or greater in a fuel composition. As an even further example, the fuel additive may be present in an amount from about 5000 ppm to about 10,000 ppm in a fuel composition

In another embodiment, the fuel additive may be oxidized. For example, the fuel additive may be oxidized to a positively charged radical or cation.

In another embodiment, the present disclosure provides compositions containing compounds with aromatic ring systems, i) having electron-releasing substituents on the ring that impart sufficient charge pressure on the ring to cause the p-orbitals of the ring to become larger and more diffuse in order to spread out this negative charge over a larger space volume and further away from the positively charged nuclei of the atoms involved, and/or ii) having features that limit or disrupt delocalization of charge out of the ring that may occur through conjugation with matching substituent p-orbitals.

Fuels

The fuel additives described herein may be combined with one or more fuels and/or one or more base oils. Suitable fuels may comprise any known hydrocarbon fuel or mixtures thereof. Suitable fuels may include one or more of gasoline, diesel fuel, middle distillate fuel, biodiesel fuel, an alcohol, such as but not limited to methanol, ethanol, bioethanol, a biobutanol, an aviation fuel, jet fuel, marine fuel, bunker fuel, burner fuel, home heating oil (for example, home heating oil no. 6), a gas-to-liquid (GTL) base oil, a Group I base oil, a Group II base oil, a Group III base oil, a Group IV base oil, an ester, a vegetable oil, and mixtures thereof.

Gasolines

The fuel used in the fuel composition embodiments of the present disclosure may comprise a petroleum hydrocarbon useful as a fuel, e.g., gasoline, for internal combustion engines. Such fuels typically comprise mixtures of hydrocarbons of various types, including straight and branched chain paraffins, olefins, aromatics, and naphthenic hydrocarbons, and other liquid hydrocarbonaceous materials suitable for spark ignition gasoline engines.

These compositions are provided in a number of grades, such as unleaded and leaded gasoline, and are typically derived from petroleum crude oil by conventional refining and blending processes such as straight run distillation, thermal cracking, hydrocracking, catalytic cracking, and various reforming processes. Gasoline may be defined as a mixture of liquid hydrocarbons or hydrocarbon-oxygenates having an initial boiling point in the range of about 20 to 60° C. and a final boiling point in the range of about 150 to 230° C., as determined by the ASTM D86 distillation method. The gasoline may contain other combustibles such as alcohol, for example methanol or ethanol.

The combustible fuels used in formulating the fuel compositions of the present disclosure may include any combustible fuels suitable for use in the operation of direct injection gasoline engines such as leaded or unleaded motor gasolines, and so-called reformulated gasolines which typically contain both hydrocarbons of the gasoline boiling range and fuel-soluble oxygenated blending agents (“oxygenates”), such as alcohols, ethers, and other suitable oxygen-containing organic compounds. Preferably, the fuel is a mixture of hydrocarbons boiling in the gasoline boiling range. This fuel may consist of straight chain or branch chain paraffins, cycloparaffins, olefins, aromatic hydrocarbons, or any mixture of these. The gasoline can be derived from straight run naptha, polymer gasoline, natural gasoline, or from catalytically reformed stocks boiling in the range from about 80 to about 450° F. The octane level of the gasoline is not critical and any conventional gasoline may be employed in the practice of this invention.

Oxygenates suitable for use in the present invention include methanol, ethanol, isopropanol, t-butanol, mixed C₁ to C₅ alcohols, methyl tertiary butyl ether, tertiary amyl methyl ether, ethyl tertiary butyl ether and mixed ethers. Oxygenates, when used, will normally be present in the base fuel in an amount below about 30% by volume, and preferably in an amount that provides an oxygen content in the overall fuel in the range of about 0.5 to about 5 percent by volume.

Carrier Fluids/Diluents

In some embodiments, the additives or additive package may be used with a liquid carrier or induction aid. Suitable carrier fluids may include any base oil as defined herein. Further suitable carrier fluids can be of various types, such as for example liquid poly-alpha-olefin oligomers, mineral oils, liquid poly(oxyalkylene) compounds, liquid alcohols or polyols, polyalkenes, liquid esters, and similar liquid carriers. Mixtures of two or more such carriers can be employed.

Other Additives

Additive compositions described herein may further comprise at least one member selected from the group consisting of: an anti-icing additive, an antiknock additive, an antioxidant, an antistatic additive, an anti-valve-seat recession additive, an antiwear agent, a biocide, a carrier fluid, a cetane improver, a combustion improver, a conductivity improver, a corrosion inhibitor, a dehazer, a demulsifier, a detergent, a dispersant, a drag reducing agent, a dye, an emulsifier, a foam inhibitor, a fuel stabilizer, an injector deposit control additive, a lubricity additive, a marker or customer-specific “tag”, a metal deactivator, an octane improver, a pour point depressant, a reodorant, a seal swell additive, a surfactant, a wax anti-settling additive (a “WASA”), and a mixture thereof.

Combustion Improvers

Suitable combustion improvers may comprise one or more of a manganese compound, ferrocene, platinum, cerium, cerium oxide, and the like. For example, a non-limiting example of a useful manganese compound is an alkylcycloalkyldienyl manganese tricarbonyl, such as methylcyclopentadienyl manganese tricarbonyl. It generally is added in treat rates of about 0.0156 to about 0.125 gram of manganese per gallon of fuel.

Cyclopentadienyl manganese tricarbonyl compounds such as methylcyclopentadienyl manganese tricarbonyl are suitable combustion improvers because of their outstanding ability to reduce tailpipe emissions such as NO_(x) and smog forming precursors and to significantly improve the octane quality of gasolines, both of the conventional variety and of the “reformulated” types.

Corrosion Inhibitors

A variety of materials are available for use as corrosion inhibitors in the practice of embodiments disclosed herein. Thus, use can be made of dimer and trimer acids, such as are produced from tall oil fatty acids, oleic acid, linoleic acid, or the like. Another useful type of corrosion inhibitor for use in the practice of this invention are the alkenyl succinic acid and alkenyl succinic anhydride corrosion inhibitors such as, for example, tetrapropenylsuccinic acid, tetrapropenylsuccinic anhydride, tetradecenylsuccinic acid, tetradecenylsuccinic anhydride, hexadecenylsuccinic acid, hexadecenylsuccinic anhydride, and the like. Also useful are the half esters of alkenyl succinic acids having 8 to 24 carbon atoms in the alkenyl group with alcohols such as the polyglycols. Further suitable materials are the aminosuccinic acids or derivatives thereof, such as a tetralkenyl succinic acid.

Demulsifiers

A wide variety of demulsifiers may be suitable for use with embodiments disclosed herein, including, for example, polyoxyalkylene glycols, oxyalkylated phenolic resins, and like materials.

Detergents

Metal-containing or ash-forming detergents function both as detergents to reduce or remove deposits and as acid neutralizers or corrosion inhibitors, thereby reducing wear, deposits and corrosion and extending engine life for engines combusting fuel formulations. Detergents generally comprise a polar head with a long hydrophobic tail where the polar head comprises a metal salt of an acidic organic compound. The salts may contain a substantially stoichiometric amount of the metal, in which case they are usually described as normal or neutral salts, and would typically have a total base number or TBN (as measured by ASTM D2896) of from 0 to less than 150. Large amounts of a metal base may be included by reacting an excess of a metal compound such as an oxide or hydroxide with an acidic gas such as carbon dioxide. The resulting overbased detergent comprises micelles of neutralized detergent surrounding a core of inorganic metal base (e.g., hydrated carbonates). Such overbased detergents may have a TBN of 150 or greater, and typically ranging from 250 to 450 or more.

Suitable detergents for use in some embodiments may comprise one or more of Mannich base detergents, polyetheramines, PIB-amines, succinimides, and combinations thereof.

Friction Modifiers and Lubricity Additives

For certain applications it may be desirable to use one or more friction modifiers also referred to as lubricity additives in preparing the finished fuel formulation. Suitable lubricity additives include such compounds as aliphatic fatty acid amides, aliphatic carboxylic acids, aliphatic carboxylic esters, aliphatic carboxylic ester-amides, aliphatic amines, or mixtures thereof. The aliphatic group typically contains at least about eight carbon atoms so as to render the compound suitably fuel soluble. Also suitable are aliphatic substituted succinimides formed by reacting one or more aliphatic succinic acids or anhydrides with ammonia.

The use of lubricity additives is optional and will depend of the inherent lubricity of the fuel. However, in applications where friction modifiers are used, finished fuel formulations may contain up to about 1.25 wt %, and usually from about 0.05 to about 1 wt % of one or more friction modifiers.

Inhibitors

Finished fuel compositions as described herein may in some embodiments contain some inhibitors. The inhibitor components serve different functions including corrosion inhibition and foam inhibition. The inhibitors may be introduced in a pre-formed additive package that may contain in addition one or more other components used in the finished fuel compositions. Alternatively these inhibitor components may be introduced individually or in various sub-combinations. While amounts of inhibitors used may be varied within reasonable limits, the finished fuel compositions of this disclosure will typically have a total inhibitor content in the range of about 0 to about 15 wt %, on an “active ingredient basis,” i.e., excluding the weight of inert materials such as solvents or diluents normally associated therewith.

The following examples further illustrate aspects of the present disclosure but do not limit the present disclosure.

EXAMPLES

Octane engine measurements were used to characterize the impact of electron-releasing groups on the rings of aromatic fuel additive compounds. Thus the ability of a ring to hold onto or lose electrons when subjected to the appropriate environmental stimulations was determined. Specifically, it was found that the research octane number (RON) and motor octane number (MON) both increase with the increasing ability of an additive to hold onto and/or attract electrons, and both decrease with the ease of electron loss from the additive. In the case of arylamine-based additives, it was found that electron pressure on the aromatic ring by electron-releasing substituents initially increases the ability of the additive compound to hold onto and/or attract electrons. This is reflected in an increasing positive change in RON and MON, with the RON change being the more symptomatic of this characteristic (see Table 1 below). Substituents in the para- and amine nitrogen positions of the arylamine were found to promote this behavior. Meta-substitution was found to be less effective and ortho-substitution the least. This is illustrated in Table 1, additive numbers 2 (ortho-) and 3 (para-). Table 1 also contains data that demonstrates that substituents capable of imparting higher electron pressures to the aromatic ring, i.e. a methoxy- versus a methyl-substituent on the ring (see additives 3, and 4), increase the ability of the aromatic ring to retain electrons.

TABLE 1 Use of Octane Measurements To Determine the Ability of an Aromatic Ring to Hold Onto Or Lose Electrons Treat Concentration Additive Test Compound Molecular (5000 mg/L) No. Test Compound Structure Weight Δ RON Δ MON 1 N-Methylaniline

107 0.8 0.4 2 N-Methyl-o-toluidine

121 0.3 0.4 3 N-Methyl-p-toluidine

121 1.2 0.8 4 N-Methyl-p-methoxyaniline

137 1.8 0.2 5 2,4,6-Trimethyl-N-methylaniline

149 0 −0.8 6 Naugalube ® TMQ*

174 −0.4 −1.1 7 2-Methylindoline

133 −0.2 −1.4 8 Ethanox ® 4720**

120 −0.4 −2.1 *Naugalube ® TMQ, available from Chemtura, is a polymerized 1,2-dihydro-2,2,4-trimethylquinoline. **Ethanox ® 4720, available from Afton Chemical Corporation, is a N,N′-di-sec-butyl-p-phenylenediamine. ***The “Δ” symbol refers to the change in octane number due to the presence additive in the base fuel.

What was even more surprising, however, was the turnaround of this behavior by further increasing electron pressure on the aromatic ring by increasing the number of electron-releasing substituents on the aromatic ring, and/or by decreasing the ability of the aromatic ring to spread out ring charge through extended delocalization over the maximum number of atoms. RON and MON results of additive number 5 in Table 1 demonstrate this turning point. Further, when the methyl substituents in additive number 5 are sequentially replaced by methoxy groups, both RON and MON decrease in step with the changes, however, with MON being the more symptomatic parameter tracking this behavior. An increasing negative Δ-MON as shown in Table 1 is a measure of the additive's ability to lose electrons, which is a key feature of embodiments of the present disclosure. The π-orbitals of an aromatic ring become larger and more diffuse hence enabling the π-electrons to reside much further away from the positively charged nucleus of the ring atoms. The more extensive the degree of freedom for the electrons, the easier it is for the electrons to be removed from the additive molecule. An aromatic molecule in such a state can be oxidized very easily (i.e., stripped of electrons) by chemical and/or physical means.

Results for additive number 6, a quinoline derivative, and additive number 7, an indoline derivative, indicate that features disrupting extensive delocalization of electrons in the molecule, by restricting the degrees of freedom of the amine nitrogen atom geometry with respect to the aromatic ring, can also result in an increasing negative Δ-MON. The quinoline feature ties the amine nitrogen in a six membered ring and the indoline in a five membered ring. As the ring size decreases from six to five members so does the Δ-MON from −1.1 for the Naugalube® TMQ to −1.4 for the indoline. This is as a result of the amine nitrogen being restricted from orienting its p-orbital parallel to the six p-orbitals of the benzene ring, a configuration that facilitates maximum delocalization of the π-electrons.

The results in Table 1 demonstrate that for an organic additive compound to be capable of the dual function of promoting fuel atomization by jet shear force electron-stripping and also enhance ignition by pre-charging the fuel vapor, it must show a large negative Δ-MON in the octane engine. This can be achieved by increasing electron pressure past a certain point on the aromatic ring with electron-releasing substituents, and/or by disrupting any extended delocalization of the ring electrons to substituents on the aromatic ring.

Physical shear forces that give rise to charge stratification can be created around a fuel jet exiting an injector nozzle at pressures above about 1000 Bar. Current advanced diesel engines operate at fuel injection pressures between about 1000 to about 2000 Bar (about 14,504 to about 29,008 psi), with developments underway to achieve about 2500 Bar (about 36,260 psi).

Embodiments of this disclosure take advantage of the trend toward further elevation of fuel injection pressure to exploit the powerful shear forces generated by this high injection pressure to strip electrons from additive molecules designed to exhibit a large negative Δ-MON in the octane engine.

Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. As used throughout the specification and claims, Gab and/or “an” may refer to one or more than one. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, percent, ratio, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

1. A fuel composition comprising: (a) a major amount of a fuel and (b) a minor amount of an additive composition comprising at least one fuel additive comprising an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein —X— comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring, wherein the at least one second substituent comprises at least one of an alkyl group, an alkoxy group, and an amino group, wherein the at least one fuel additive is present in an amount from about 500 ppm or greater in the fuel composition.
 2. The fuel composition of claim 1, wherein the at least one second substituent is attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent.
 3. The fuel composition of claim 1, further comprising at least one second fuel additive comprising an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein —X comprises a heteroatom and wherein R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent, wherein the at least one second substituent comprises the structure —X—R, wherein —X— comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group.
 4. The fuel composition of claim 3, wherein the fuel composition provides both enhanced fuel atomization and enhanced fuel ignition.
 5. The fuel composition of claim 1, wherein the heteroatom comprises at least one member selected from the group consisting of the group 14 elements, the group 15 elements, and the group 16 elements.
 6. The fuel composition of claim 1, wherein the heteroatom comprises at least one element selected from the group consisting of nitrogen and oxygen.
 7. The fuel composition of claim 1, wherein R comprises at least one of methyl, ethyl, propyl, and isopropyl.
 8. The fuel composition of claim 1, wherein the at least one second substituent comprises an alkyl group having up to about 32 carbon atoms, wherein the alkyl group comprises a straight or branched chain, and is saturated or unsaturated.
 9. The fuel composition of claim 1, wherein the at least one second substituent comprises at least one of methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, and pentyl.
 10. The fuel composition of claim 1, wherein the aromatic ring comprises at least one of a monocyclic ring, a polycyclic ring, and a heterocyclic ring.
 11. The fuel composition of claim 1, wherein the aromatic ring comprises at least one of benzene, naphthalene, and anthracene.
 12. The fuel composition of claim 1, wherein the additive compound comprises at least one of a member selected from the group consisting of 2,4,6-trimethyl-N-methylaniline; polymerized 1,2-dihydro-2,2,4-trimethylquinoline; 2-methyl indoline; N,N′-di-sec-butyl-p-phenylenediamine; methyl substituted benzenes; ethyl substituted benzenes; propyl substituted benzenes; isopropyl substituted benzenes; butyl substituted benzenes; and isobutyl substituted benzenes.
 13. The fuel composition of claim 1, wherein the at least one fuel additive is present in an amount from about 4000 or greater in the fuel composition.
 14. A method for enhancing fuel ignition, comprising: providing a fuel composition to a combustion system, wherein the fuel composition comprises a fuel and at least one fuel additive, wherein the at least one fuel additive comprises an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure X—R, wherein X comprises a heteroatom and wherein R comprises at least one of an alkyl group, an alkoxy group, and an amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring in the ortho and/or para position relative to the first substituent, wherein the at least one second substituent comprises the structure —X—R, wherein —X— comprises a —CH₂— or a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and an amino group; wherein the fuel ignition of the fuel composition is enhanced relative to a fuel free of the at least one fuel additive.
 15. A method of enhancing fuel atomization, comprising: (a) providing a fuel composition, wherein the fuel composition comprises a fuel and at least one fuel additive, wherein the at least one fuel additive comprises an aromatic ring having: (1) a first substituent attached to a carbon atom of the aromatic ring, wherein the first substituent comprises the structure —X—R, wherein —X comprises at least one of a —CH₂— and a heteroatom and wherein —R comprises at least one of an alkyl group, an alkoxy group, and amino group, and (2) at least one second substituent attached to a carbon atom of the aromatic ring, wherein the at least one second substituent comprises at least one of an alkyl group, an alkoxy group, and an amino group; and (b) delivering the fuel composition to a combustion area of a combustion system, wherein the delivery of the fuel composition to the combustion area causes the fuel composition to experience a shear force sufficient to remove at least one electron from the fuel additive to provide a resulting fuel additive; wherein the fuel atomization of the fuel composition is enhanced relative to a fuel free of the at least one fuel additive.
 16. The method of claim 15, wherein the delivery of the fuel composition to the combustion area is at a pressure greater than about 1000 bar.
 17. The method of claim 15, wherein the delivery of the fuel composition to the combustion area is at a pressure greater than about 1500 bar.
 18. The method of claim 15, wherein the delivery of the fuel composition to the combustion area is at a pressure greater than about 2000 bar.
 19. The method of claim 16, wherein the pressure is in the range of from about 1000 to about 2500 Bar.
 20. The method of claim 15, wherein the resulting fuel additive has been oxidized.
 21. The method of claim 20, wherein the resulting fuel additive has been oxidized to a radical.
 22. The method of claim 20, wherein the resulting fuel additive has been oxidized to a positively charged radical.
 23. The method of claim 20, wherein the resulting fuel additive has been oxidized to a positively charged cation.
 24. The method of claim 15, wherein the combustion area of the combustion system is selected from the group consisting of internal combustion engines, boilers, furnaces, incinerators, jet engines, and rocket engines.
 25. A method for enhancing fuel ignition comprising providing to the combustion area of a combustion system a fuel composition comprising a fuel additive, wherein the fuel additive decreases the fuel MON and/or RON. 